On 11 February 2016 at 11:53, H.J. Lu <hjl.to...@gmail.com> wrote: > Since this isn't Plain Old Data (POD) for the purposes of layout, it > isn't covered by my proposal for psABI. I leave this to C++ ABI.
You never define "POD for the purposes of layout", and I can only interpret it as being equivalent to "standard-layout". The property of being trivially copyable/destructible is not a statement about layout and my EmptyInt example is POD in every other aspect. There's a good argument for trivially copyable/destructible being the relevant property: it means an object can be copied simply by copying its bytes and destroyed simply by discarding its storage. If the object occupies no storage (other than padding) then these operations become nops hence there is never a need to have a pointer/reference to the original object. The precise layout is not really important here, e.g. struct U is unusually large considering its lack of data members, due to the need for padding between its base classes, but this doesn't change the fact it can be copied using no operation (and g++ indeed does). Matthijs van Duin
